Closed vessel curing of concrete



United States Patent 2,917,778 CLOSED VESSEL CURING OF CONCRETE LutherL. Lyon, Jr., and Ray W. Qualley, Wichita, Kans., assignors to TheColeman Company, Inc., Wichita, Kans., a corporation of Kansas NoDrawing. Application December 23, 1955 Serial No. 554,921

3 Claims. (Cl. 18-475) This invention relates to the closed vesselcuring of concrete lined vessels.

The lining of vessels with concrete has been carried on for many yearsand such concrete linings have been found to be particularly useful inconnection with water heaters and other vessels. One problem that haspersisted is that during the first two or three weeks of use the exitwater from the tank has increased hardness, alkalinity, and in somecases produces milky water. Immediate air drying of the concrete liningtends to improve the liner from the standpoint of reducing hardness,alkalinity and milky exit water, but, unfortunately, exposure of theconcrete liner to air flow brings about unsatisfactory curing of theconcrete, resulting in low strength concrete.

As illustrative of prior art practices in the lining of containers, FordPatent No. 2,395,731 may be referred to. A more recently developedcommercial practice is dc scribed in the copending application of ArthurE. Phillips, Serial No. 363,843, filed June 24, 1953.

An object of the present invention is to provide a process in which theconcrete liner of a vessel is effectively cured, while at the same timereducing hardness, alkalinity, and milky exit water. A further object isto provide a process in which enough moisture is maintained within thetank to produce good curing of the concrete liner therein even when thetank is closed, as by plugging the tank openings thereof, thus bringingabout effective curing of the concrete liner, While reducing alkalinityand hardness, as above described. Other specific objects and advantageswill appear as the specification proceeds.

In one embodiment of our invention, we take a vessel which has beenfreshly lined with concrete by any of the common methods, and introduceinto the vessel carbon dioxide in sufficient quantity to neutralize thelayer of calcium hydroxide on the surface of the concrete, thereaftersealing the vessel and curing the concrete out of access to outside air.A convenient method of introducing the carbon dioxide is to insert apellet of Dry Ice into the vessel immediately after the liner is formedand promptly thereafter corking the openings of the vessel so as toprovide an air seal. The closed vessel brings about a cure of theconcrete under moist conditions, giving time for calcium aluminumsilicates to form, and the slow recrystallization thus accomplishedproduces a sturdy liner for the vessel. At the same time, the atmospherecontaining a substantial volume of CO produces an insoluble layer on theinside, consisting principally of calcium carbonate, thus reducinghardness, alkalinity and milky exit water.

As a specific example of the embodiment described, the followingoperation may be set out: The vessel, such as, for example, a waterheater shell, which is provided with openings such as an inlet openingand a drain opening and sometimes with inspection openings, is providedwith a concrete mixture adapted to form the liner within the vessel.This mixture may consist of Portland cement, said, water, etc., andafter the mixture is introduced into "ice the tank, the tank assembly isplaced upon a spinning machine and secured in position, the openingsbeing sealed. The tank is then rotated at an rpm. which will result in aperipheral speed of, say, 3,000 feet per minute, for 15 seconds, afterwhich time the tank may be vibrated, as by hammering the outside wallsof the tank as the tank continues to spin. The rotation of the tank maythen be stopped, the plug from the drain opening removed, and the sludgeallowed to run off. The plug may then be replaced and the spinning drivestarted again and the tank hammered or vibrated as it is spinning, thedrain plug again removed and the residue drawn of. A Dry Ice pellet, orseveral pellets, may then be introduced into the tank and the tanksealed so as to exclude air from the interior.

After curing for several days under the moist conditions described, anextremely sturdy concrete liner is produced, in which hardness,alkalinity, and tendency to produce milky exit water is reduced.

The carbon dioxide may be introduced in any suitable form, either as aDry Ice pellet or as gaseous 00,. For example, combustion gases may beintroduced into the tank to supply the desired CO, content.

The amount of CO introduced into the tank will vary under differentconditions. It is sufficient that the CO present in the tank be enoughto neutralize the layer of calcium hydroxide which is on the surface ofthe concrete. Ordinarily, for a tank having approximately 2100 squaresinches of concrete surface, 0.25 cubic feet of CO, at atmosphericpressure and room temperature is sufficient to bring about suchneutralization. On the volume basis, we desire to have the CO be atleast 15% of the total volume in the tank chamber. Generally, on asurface basis, we find that one cubic foot of CO: at atmosphericpressure and room temperature is satisfactory for every 40 to squarefeet of surface. Highly effective results have been attained when onecubic foot of CO, at atmospheric pressure and room temperature isemployed for every 60 square feet of surface. As above stated, however,the amount of CO employed will vary 'with different conditions, and itis necessary only that the amount of available CO within the chamberbring about a neutralization of the calcium hydroxide on the surface ofthe concrete.

We prefer to introduce the CO promptly after the application of theconcrete to the surface, and thus at the very beginning of the curingstage. While some delay in the period of application is permissible, weprefer to make the application within a matter of minutes after thespinning or other concrete applying operation is completed, andthereafter we desire to carry on the curing operation in the absence ofoutside air.

Detailed examples of the process may be set out as follows:

Example I A water heater tank was lined with concrete to provide aninner concrete surface of about 2100 square inches. A mix containing 22%of Portland cement, 63% of pure sifted sand, and 13% of water, all on aweight basis, was supplied through an opening into the vessel and thetank assembly was placed upon the spinning machine and rotated to give aperipheral speed of 3,000 feet per minute for 15 seconds. After spinningthe tank for 15 seconds, the tank was hammered to vibrate the same as itcontinued to spin. After a short vibration period, the rotation wasstopped and the plug from the drain opening removed and the sludgeallowed to run off. A new spinning operation was then carried on withfurther vibrating or hammering, and the spinning then discontinued. Thedrain plug was again removed and the residue drained off. Two pellets ofDry Ice were then introduced into the interior of the tank, each pelletbeing about one-half inch in diameter and two inches in length. Theopenings were then corked so as to cut off access to the atmosphere, andthe concrete was then allowed to cure under moist conditions and out ofcontact with outside air. In this instance, the curing-was for 28 days.It was found that the hardness of the liner decreased by a factor of andthe alkalinity, as measured by pH, decreased by 2 to 3 pH units, whileat the same time a minimum of milky water was produced.

Example II The process was carried on as described in Example I exceptthat 4 pellets of Dry Ice were employed, giving approximately 0.5 cubicfeet of carbon dioxide. The results were comparable to those describedin Example I.

Example III The process was carried on as described in Example I, exceptthat 6 of the pellets of Dry Ice were used, giving a carbon dioxidecontent of 0.75 cubic feet. Excellent results were obtained as describedin Example I.

Example IV Here, in place of Dry Ice, gaseous CO was employed and theuse of the introduced gaseous C0, gave results comparable to thosedescribed in Example I.

In addition to the foregoing Examples, CO was introduced into thevessels in the form of combustion gases. Good results were obtained.

While the invention is described for simplicity of illustration inconnection with a water heater tank, it will be understood that otherclosed vessels employed for many different purposes may be employed inthe carrying out of the process, the long curing of the concrete undermoist conditions being carried on to produce an extremely sturdy linerin which the hardness, alkalinity, and tendency to form milky exit waterwas substantially reduced.

While, in the foregoing specification, we have set forth process stepsin considerable detail for the purpose of illustrating embodiments ofthe process, it will be understood that such details of procedure may bevaried wide 4 1y by those skilled in the art without departing from thespirit of our invention.

We claim:

1. In a process for curing a wet concrete liner within a water tank, thesteps of introducing into the tank CO in the proportion of one cubicfoot of CO, at atmospheric pressure and room temperature for 40-80square feet of concrete surface, the said CO; providing at least about15% of the atmosphere within the tank, sealing the tank to excludeaccess of air, and curing the concrete under the moist conditionsprevailing in the sealed tank and for a period up to about 28 days.

2. The process of claim 1, in which the proportion of CO is about onecubic foot at atmospheric pressure and room temperature for each squarefeet of concrete surface.

3. In the fo-rrning of a concrete lined water heater tank in which aconcrete mix is introduced into the tank and the tank sealed and spun toapply the concrete to the walls of the tank, the excess liquid in thetank being then drained off, the steps of introducing solid C0 in theproportion of one cubic foot at atmospheric pressure and roomtemperature for each 60 square feet of concrete surface, the said COproviding about at least 15% of the atmosphere within said tank, sealingthe tank against the ingress of air, and curing the concrete under themoist conditions prevailing in the sealed tank for a period up to about28 days.

References Cited in the file of this patent UNITED STATES PATENTS Re.24,187 Burwell July 31, 1956 898,703 Thom Sept. 15, 1908 1,599,413Harrison et al Sept. 14, 1926 2,496,895 Staley Feb. 7, 1950 2,720,469Serkin Oct. 11, 1955 OTHER REFERENCES Grant: Manufacture of ConcreteUnits l0, published in Concrete, August 1951, pp. 36-39.

qua

1. IN THE PROCESS FOR CURING A WET CONCRETE LINER WITHIN A WATER TANK,THE STEPS OF INTRODUCING INTO THE TANK CO2 IN THE PROPORTION OF ONECUBIC FOOT OF CO2 AT ATMOSPHERIC PRESSURE AND ROOM TEMPERATURE FOR 40-80SQUARE FEET OF CONCRETE SURFACE, THE SAID CO2 PROVIDING AT LEAST ABOUT15% OT THE ATMOSPHERE WITHIN THE TANK, SEALING THE TANK TO EXCLUDEACCESS OF AIR, AND CURING THE CONCRETE UNDER THE MOIST CONDITIONSPREVAILING IN THE SEALED TANK AND FOR A PERIOD UP TO ABOUT 28 DAYS.